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Plasmids of the pRM/pRF family occur in diverse Rickettsia species

Gerald D Baldridge1, Nicole Y Burkhardt, Roderick F Felsheim

  • 1Department of Entomology, University of Minnesota, 1980 Folwell Ave., St. Paul, MN 55108, USA. baldr001@umn.edu

Applied and Environmental Microbiology
|December 11, 2007
PubMed

Insights

Plasmids have been discovered in several Rickettsia species, challenging previous beliefs. These Rickettsia plasmids carry genes similar to those found on previously identified plasmids, suggesting conserved functions across species.

Area of Science:

  • Bacteriology
  • Genetics
  • Molecular Biology

Background:

  • The genus Rickettsia was historically considered to lack plasmids, a long-held dogma.
  • Recent discoveries of plasmids in Rickettsia felis (pRF) and Rickettsia monacensis (pRM) have challenged this notion.

Purpose of the Study:

  • To investigate the presence and characteristics of plasmids in additional Rickettsia species.
  • To compare the genetic content of newly identified Rickettsia plasmids with known plasmids pRF and pRM.

Main Methods:

  • Pulsed-field gel electrophoresis (PFGE) to analyze plasmid sizes and compare mobilities.
  • Southern blot hybridization to detect specific gene sequences on the plasmids.
  • Long-term serial passage in cultured cells to assess plasmid stability.

Main Results:

  • Plasmids were identified in Rickettsia helvetica, R. peacockii, R. amblyommii, and R. massiliae from ixodid ticks, and R. hoogstraalii from an argasid tick.
  • R. peacockii and R. amblyommii plasmids showed similar migration patterns to pRM and pRF.
  • R. massiliae plasmid lacked a heat shock gene and was the smallest; R. hoogstraalii plasmid showed similarity to pRM and contained unique transporter and stringent response genes.

Conclusions:

  • The findings confirm the widespread presence of plasmids in Rickettsia, extending beyond previously known species.
  • Rickettsia plasmids exhibit conserved and unique gene content, indicating diverse functional roles.
  • Plasmid stability varies, as demonstrated by the loss of plasmids in R. peacockii during cell culture passage.

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